Getting Started
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2
Introduction to On-Board Diagnostics
OBD II
On-board diagnostics version II (OBD II) is a system that the Society of
Automotive Engineers (SAE) developed to standardize automotive
electronic diagnosis.
Beginning in 1996, most new vehicles sold in the United States were
fully OBD II compliant.
✓ Technicians can now use the same tool to test any OBD II
compliant vehicle without special adapters. SAE established
guidelines that provide:
❒ A universal connector, called the DLC, with dedicated pin
assignments.
❒ A standard location for the DLC, visible under the dash on driver’s
side.
❒ A standard list of diagnostic trouble codes (DTCs) used by all
manufacturers.
❒ A standard list of parameter identification (PID) data used by all
manufacturers.
❒ Ability for vehicle systems to record operating conditions when a
fault occurs.
❒ Expanded diagnostic capabilities that records a code whenever a
condition occurs that affects vehicle emissions.
❒ Ability to clear stored codes from the vehicle’s memory with a
Scan Tool.
SAE Publications
SAE has published hundreds of pages of text defining a standard
communication protocol that establishes hardware, software, and
circuit parameters of OBD II systems.
• SAE publishes recommendations, not laws, but the Environmental
Protection Agency (EPA) and California Air Resources Board
(CARB) made many of SAE’s recommendations legal requirements.
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